the suspects were apprehended. >> yeah. there is been some conflicts in this.nbc'spetewilliamsconfirmedthat at least one of them was spotted and is believed to be a pressure cooker-type bomb, a pressure cooker from your standard kitchen filled with some sort of powder and perhaps projectiles. at other times, they were described as having something like grenades or improvised explosives. i've seen some reports in the last few minutes that there are believed to be undetonated explosive devices in the watertown area. that's why they're trying to get people as far away as possible. >> chris, thank you very much. we'll have more from nbc news's chris palone in the program. a quick check off markets for you. global markets are taking these event necessary stride. we know very little still about the motives, about these suspects, beyond the fact that one has been skilled and the other is on the run and authorities are trying, of course, to resolve this situation there. we'll be right back. stay with us here on "worldwide exchange." >>> welcome to "worldwide exchange." a manhunt is under way f

the chechen rebels are denying that there is any link to that. in addition to that, this isperpetewilliamsofnbc news. he now reports that the boston marathon bomber manhunt is now down to one person, the younger brother. initially, earlier today, there was some speculation that perhaps there was a third suspect. that is now being downplayed. and pete williams reports that the manhunt down to one person. in addition to that, the police officials are now telling pete williams that during the early morning watertown gun battle between police and the two brothers, about 200 rounds were exchanged. they have found seven ieds, improvised devices, that have been removed, in searches so far in watertown and also some from the house in cambridge. in addition to that, we have obtained these pictures from the owner of a shell station, which we're going to show you right now, and i want to explain the fact that, obviously, the younger brother is in the forefront, leaving the shell station there, but we've blacked out or blurred out the face of the second individual, because we don't know that the tim

to believe that perhaps he was a victim of one of his own devices. >> and accordingtopetewilliams, boththese marathon suspects had foreign military training. let's check in once more with adam williams. he is right there in the epicenter of everything happening. >> that's right. i'm able to watch these pictures live along with you. and i can tell you that what you're seeing here, this is one street in watertown. it's playing out on many streets in watertown. my police source who has been out here late last night telling me these house to house searches are going on all over the place. it would be interesting to find out the population of watertown and the square mileage to see what they're up against. it's evident, though, ta they are taking everything, everybody very seriously. i just ran into a boston globe photographer who told me he's been roaming around on foot because we can no longer drive in or out of this community. he's been stopped by police a number of times. when he was changing the camera in the car, they searched his trunk making sure that this was nothing in there. this

thedebris.petewilliamsreportsthat investigators know for certain this attack involved just two bombs. several other packages were deemed suspicious. it is coming from nbc pete williams. a senior law enforcement official says it appears there were two unbloweded devices. just two that went off. police are studying surveillance to see if they can see anybody with packages where the bombs went off. there is a video of someone carrying two backpacks but it is too early to know whether that was related to the attack. >> social media played a huge role in the last 24 hours. the aftermath of the bombings at the boston marathon. boston police confirmed the explosions in a tweet at 3:39 p.m. eastern time and provided updates and subsequent tweets throughout the afternoon and into the evening. i'm not sure this had been done before. witnesses sent updates as people around the country followed the attack. and foursquare was actually running in the marathon, the ceo. i'm okay. about 20k of us in coral just before mile 26 marker. the hashtag spiked after the attack. and google set up what's calle

this hallway blockedoff.petewilliamsisreporting that federal officials say they believe they know who sent the letters to st senate and the white house but no arrest has been made yet. they're waiting for test results. >> we're going to hear from jay carney sometimes in the past few minutes about either boston or developments in washington or both. just as someone who reports to the area every day, can you give us an idea of how different security looked? >> it doesn't have the mi militarized feel. yesterday we had a parade that didn't appear that different at all. today coming up here to capitol hill all of the trash cans in the parks have been taking off their bases and knocked over on their sides. clearly they're going to go around and collect those and provide one less place for somebody to hide a gis and staffers are feeling jittery. we have a couple of these incidents. you can imagine people are on heightened alert. a lot of peoplery saying it feels reminiscent of the post 9/11 era. >> don't go too far. they think they may know who sent at least some of these letters. can you add any

thatpetewilliamsfromnbc news was insistent all the way through, that his law enforcement sources, which, of course, are impeccable were saying that there was not a suspect in custody. what was going on yesterday and what continues to go on today is that authorities have pored through the video and pictures have been coming in over the last three days trying to pinpoint exactly where those two packages were placed before they went off. now, authorities do acknowledge to nbc news that they have identified by sight a person who is seen placing either a backpack or a duffel bag on to the ground in the place where the second bomb went off in the moments leading up to that explosion. however, according to nbc news, that person has not been identified by name. they just see him on the tape and are working to identify him. he certainly has not been arrested or put into custody. police continue their work today to try to figure out exactly who that person is. last night, the fbi was planning to have one of their twice daily media briefings around 8:00 local time. that was canceled. and so we're